In short, the best compromise is a factory tuned machine.
Not for me. The stock bike didn't run well enough for me. Now it does. And yes, as I've said in a different post, it uses around 5% more fuel in the process but that's only because I had it tuned for max torque and power. Set up to run a bit leaner (more like stock, but not quite as lean) I have no doubt whatsoever that it would have used less fuel than a stock bike and still made considerably more power. But I have no desire to prove this as I'm happy the way it is - 5% more fuel is a small price to pay for the way it runs now. I don't ride bikes for economy, I ride them for fun.
In 38+ years of riding & messing with my intake, jetting, and exhaust, I have NEVER seen increased mileage as a result.
The crucial word there is 'jetting'. You're talking about carburettor engines, where the control of fuelling is crude and it's simply not possible to have them running so lean while still remaining healthy and rideable. With an injected bike, improving the breathing (induction and exhaust) WILL improve economy IF the fuelling is set up apropriately. How could it not? If the engine requires less power to suck air in and push exhaust gasses out you'll have more power available to drive the bike, meaning you need to open the throttle slightly less, meaning less fuel used.
I think it's purely academic to propose that fuel economy AND performance can be increased by messing with a factory tuned bike; in the real world..... it ain't happening.
The Bandit is the first of a large number of injected bikes that I've tuned that HASN'T seen an improvement in economy. I saw improvements on various BMWs, a Blackbird, a Triumph and.....well, a number of others.
In the real world, factories are doing an absolutely FANTASTIC job giving us an environmental friendly lean and green running machine. Our HUGE mufflers are incredibly efficient at flowing the exhaust while keeping the noise to a minimum.... And MY GOD the power modern bikes are putting out!!!
Yes, they're doing a fantastic job, but every bike that rolls off every production line in the civilised world is compromised by its need to comply with regulations. That means there is scope for improvement - the factory engineers know this perfectly well but their hands are tied.
Why do you think that bikes like the Ducati 1098R, Aprilia Mille Factory and a few other top end bikes are delivered to their customers with a second set of cans and a different ECU marked "for track use only"? What Ducati and the others are saying is "Here's a bike that's legal for us to sell and you to buy. But if you want it the way we designed it, fit these other bits because it'll go much better." Those other bits (can(s) and some method of adjusting the fuelling) are what so many people fit to their bikes because they know that the stock bikes are compromised and they want to realise a bit more of their bike's potential.
Sure, modern sports bikes put out a lot of power, but if they comply with regulations when sold there's always going to be a bit more available. And that's what draws people to tinker with them.
I mean, a mere 104hp and 84ft.lb's of torque, and a top speed of 145+ mph, just isn't enough.
Rooooight......
104bhp from 1255cc just isn't trying. It's the vast, untapped potential of the Bandit motor that means it's crying out for tuning. You try riding a 130bhp 1250 Bandit with absolutely no flat spots or surging - believe me, you'll never want to go back to what you've got. So, we can't improve on Suzuki's stock bike? Pah!
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It's like I'm riding 2 or 3 up all the time!! 
